Semiconductor device having aluminum contacts or vias and method of manufacture therefor

ABSTRACT

A semiconductor device and a method of manufacture therefor. The semiconductor device includes: (1) a substrate having a recess therein, (2) an aluminum-alloy layer located over at least a portion of the substrate and filling at least a portion of the recess and (3) a protective metal layer at least partially diffused in the aluminum-alloy layer, the metal protective layer having a high affinity for oxygen and acting as a sacrificial target for oxygen during a reflow of the aluminum-alloy layer.

This Application is a Divisional of prior application Ser. No.08/820,063 filed on Mar. 18, 1997, currently pending, to Sailesh M.Merchant, et al. The above-listed Application is commonly assigned withthe present invention and is incorporated herein by reference as ifreproduced herein in its entirety under Rule 1.53(b).

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to semiconductors andfabrication techniques and, more specifically, to a semiconductor devicehaving a conductive layer with a metal protective layer at leastpartially diffused into the conductive layer and a method of manufacturetherefor.

BACKGROUND OF THE INVENTION

In semiconductor integrated circuits, the formation of metalinterconnect layers is important to the proper operation of suchdevices. Metal interconnect signal lines make contact to lowerconductive layers of the integrated circuit through vias or throughcontact windows to "active" device regions of the semiconductor in aninsulating layer. For best operation of the device, the metal used toform the interconnect layer should completely fill the via or contactwindow (hereinafter referred to as opening(s)).

Because of their physical properties, aluminum-alloys (e.g.,aluminum-copper, aluminum-silicon, aluminum-copper-silicon) areespecially suited for fabrication of metal interconnect lines inintegrated circuits. However, the sputtering process used to applyaluminum-alloy thin film layers to an integrated circuit generallyresults in less than ideal filling of openings. Since the aluminum-alloyis deposited at an elevated temperature to obtain large grains forimproved electromigration reliability, these large aluminum-alloy grainstend to form on the upper surface of the insulating layer. The grainsthat form at the edges of the opening tend to block the opening beforethe aluminum-alloy has a chance to completely fill it. This results invoids and uneven structures within the via.

This problem is especially acute as integrated circuit devices arefabricated using smaller geometries. The smaller openings used in thesedevices tend to have a larger aspect ratio (opening height is to widthratio) than larger geometry devices, which exacerbates thealuminum-alloy filling problem.

The uneven thickness of the aluminum-alloy layer going into the openinghas an adverse impact on device functionality. If the voids in theopening(s) are large enough, contact resistance can be significantlyhigher than desired. In addition, the thinner regions of thealuminum-alloy layer will be subject to the well known electromigrationproblem. This can cause eventual open circuits at the contacts andfailure of the device.

To solve the problems associated with sputtering techniques, manyapproaches have been used to ensure good metal contact to lowerinterconnect levels. For example, one technique involves depositing thealuminum-alloy interconnect by sputtering in a physical vapor depositiontool ("PVD")and then reflowing it in a separate reflow module attemperatures that range between 500° C. to 575° C. At thesetemperatures, the surface mobility and diffusion kinetics of thealuminum-alloy are enhanced, allowing it to deposit into the openingsand fill them. However, at these high temperatures, the reflow module isvery sensitive to impurities. As is well known, aluminum-alloy easilyoxidizes and any presence of oxygen or moisture in the tool,particularly while processing in the reflow module will negate thereflow process. In other words, the aluminum-alloy will not reflow andproperly fill the opening if the aluminum-alloy oxidizes or moistureforms on it. Thus, the deposition, transfer and subsequent reflow iscarried out in an ultra high vacuum environment, preferably in amulti-chamber cluster tool having very low partial pressures of watervapor and oxygen.

These environmental conditions require extensive preconditioning times,such as tool chamber pump-down and bakes, to bring the modules up to therequired pristine operating conditions. Further, metal vacuum seals mustbe used instead of conventional "O"-ring seals to reduce modulepump-down times. These metal seals must be used in the transfer chamberas well as in the deposition and reflow chambers. Consequently, thesepre-conditioning steps increase the overall cost of the machine and theproduction time, which also increase the overall cost of thesemiconductor devices.

Accordingly, what is needed in the art is a semiconductor device and amethod of manufacture therefor such that the conductive layersconnecting the openings are subject to not subject to substantialoxidation during the manufacturing process. The semiconductor and methodof the present invention addresses these needs.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides a semiconductor device and a method ofmanufacture therefor. The semiconductor device includes: (1) a substratehaving a recess therein, (2) a conductive layer located over at least aportion of the substrate and filling at least a portion of the recessand (3) a metal protective layer at least partially diffused in theconductive layer. In an advantageous embodiment, the metal protectivelayer has a higher affinity for oxygen than the conductive layer andthereby acts as a sacrificial "getter" of oxygen from the conductivelayer during a reflow of the conductive layer to reduce oxidation in theconductive layer. In another embodiment, the metal protective layer actsas an oxygen getter from the processing tool, and in yet anotherembodiment, the alloying element in the metal protective layer acts asan oxygen getter.

The present invention thereby introduces the broad concept of reducingor eliminating the oxidation that occurs in the conductive layer byproviding a barrier or cap, in the form of at least a partially oxidizedmetal layer that traps oxygen before it reaches the conductive layer orremoves it from the conductive layer, or in other embodiments, removesit from the conductive layer in the event that the conductive layeroxidizes prior to deposition of the metal protective layer. The presentinvention therefore allows a conductive plug to be formed reliablywithout requiring the exotic low pressure environment of the prior art.

In one embodiment of the present invention, the substrate comprisessilicon and the conductive layer may be aluminum, aluminum-alloy orother conventional or later-discovered conductive metals used forforming a circuit pattern on the semiconductor device. Alternatively,the substrate may be gallium arsenide or any other conventional orlater-discovered substrate suitable for providing a foundation for asolid state device.

In one preferred embodiment of the semiconductor device, the metalprotective layer decreases the rate of electromigration is damageaccumulation in the conductive layer when it partially diffuses into theconductive layer.

In an alternative embodiment of the present invention, the aluminum oraluminum-alloy layer fills at least the portion of the recess and formsa contact for the semiconductor device. The recess thus may be a viathat provides inter-layer connectivity in a multi-layer substrate or acontact for a terminal (such as a source, gate, drain, base, emitter orcollector) of a semiconductor device.

In one embodiment of the present invention, the metal protective layeris selected from the group consisting of: (1) magnesium, (2) yttrium,(3) hafnium, (4) cerium, (5) scandium and (6) zirconium. Those skilledin the art are familiar with other metals that may be advantageous,depending upon the application. In another embodiment, the metalprotective layer is selected from a group of metals consisting of (1)titanium or (2) vanadium, and in yet another embodiment, the metalprotective layer is selected from a group of aluminum-alloys containingany of the aforementioned metals as solute. In such an embodiment, themetal protective layer is alloyed with the aluminum or aluminum-alloyconductive layer. Each of these inventions is discussed in detail below.Those skilled in the art are familiar with other metals and alloys thatmay be advantageous, depending on the application.

In another embodiment of the present invention, the metal protectivelayer is selected from a group of metals that are able to at leastpartially reduce any oxide on the conductive layer. Moreover, theelements of the metal protective layer may be at least partiallydiffused into the conductive layer without substantially altering theintended purposes of the conductive layer. Furthermore, the metalprotective layer may be fully sacrificed during the reflow process, oralternatively, some of the original metal protective layer may remainintact.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of a semiconductor device thathas a contact window or via formed therein;

FIG. 2 illustrates a schematic diagram of a conventional physical vapordeposition tool with the various deposition chambers therein.

FIG. 3 illustrates a cross-sectional view of the semiconductor device ofFIG. 1 with a conductive layer partially deposited in the via;

FIG. 4 illustrates a cross-sectional view of the semiconductor device ofFIG. 3 with a metal protective layer deposited over the conductive layerprior to its diffusion in the conductive layer;

FIG. 5 illustrates a cross-sectional view of the semiconductor device ofFIG. 4 after the device has been subjected to a reflow process, wherethe metal layer has been oxidized and diffused into the conductivelayer.

DETAILED DESCRIPTION

Referring initially to FIG. 1, an integrated circuit device is formed ona semiconductor substrate 10, which may be comprised of materials knownto those skilled in the art such as silicon or gallium arsenide.Although a substrate 10 is described, it will be apparent to thoseskilled in the art that the described technique may be used with acontact formed to any underlying conductive layer. Thus, the substrate10 may include multiple layers of polycrystalline silicon or metallicinterconnect, as well as being an active region in a monocrystallinesilicon substrate.

An insulating layer 12 that has a thickness, which varies from device todevice, depending on the application, such as a silicon oxide (SiO₂), isformed over the substrate 10, and an opening 14 (via or contact window)is formed therethrough using a mask and an isotropic etching techniqueas known in the art.

The semiconductor device is placed in a conventional deposition tool 16,such as a physical vapor deposition tool ("PVD") schematicallyillustrated in FIG. 2, or a chemical vapor deposition tool, not shown. Abarrier layer 18, such as a refractory metal, refractory metal nitride,refractory metal silicide, or combination thereof, is uniformlydeposited over the insulating layer 12 and in the opening 14 usingconventional deposition techniques. The barrier layer 18 is preferablydeposited to a thickness of approximately 20 nm to 200 nm and ispreferably comprised of titanium and titanium nitride. A "wetting layer"to improve the aluminum-alloy deposition characteristics may also beincluded as part of barrier layer 18. Because of the innate advantagesassociated with the present invention as discussed herein, thedeposition tool 16 is preferably of conventional design. As such, thedeposition tool 16 preferably has a deposition chamber 16a in which thebarrier layer 18, is formed a deposition chamber 16c in which theconductive layer 20 is deposited, a transfer chamber 16b through whichthe semiconductor device is transferred from one chamber to another, achamber 16e and a reflow chamber 16d. The metal protective layer 22(FIG. 3) is subsequently deposited in chamber 16e and the substrate 10is heated in a reflow chamber 16d in which the conductive layer 20 isreflowed after deposition. However, it should be understood that in someembodiments, all depositions steps may be conducted in a single chamber.Alternatively, the semiconductor device may be transferred to a rapidthermal anneal ("RTA") device 24 as schematically illustrated in FIG. 2.Because the PVD tool 16 is of conventional design, special metallicseals and preparation techniques for the PVD tool, which are required byconventional processes to maintain extremely low vacuums, are notnecessary.

Turning now to FIG. 3, the semiconductor device with a conductive layer20 deposited thereon is illustrated. The deposition of the conductivelayer 20 is conducted in the PVD tool 16, and is deposited over thesubstrate 10 and the barrier layer 18 using conventional PVD techniquesat a pressure of ranging from about 1 milliTorr to about 10 milliTorrand temperatures that ranges from about 25° C. to about 400° C. Inpreferred embodiments, the thickness of the conductive layer ranges fromabout 400 nm to about 700 nm. The conductive layer 20 is susceptible tooxidation and may be comprised of any type of such conductive material,such as aluminum or aluminum-alloy, known to those skilled in the art.The purpose and function of the conductive layer 20 is well known in theart and serves as an interconnect layer that electrically connectsdevices on the semiconductor device. The conductive layer 20 is not abarrier layer, such as titanium nitride. For reasons previouslydiscussed with respect to conventional processes, the conductive layer20 is not uniformly deposited within the opening 14 and must, therefore,be reflowed so that the it can uniformly fill and contact the sides ofthe opening 14 to form a reliable contact point for the integratedcircuit device.

Upon deposition of the barrier layer 12 and the conductive layer 20, themetal protective layer 22, as illustrated in FIG. 4, is deposited overthe conductive layer 20. In a preferred embodiment, the metal layer 22is deposited using conventional PVD techniques under a pressure thatranges from about 2 milliTorr to about 10 milliTorr and a temperaturethat ranges from about 25° C. to about 400° C. and deposition isconducted to achieve a metal layer that has a thickness that ranges fromabout 5 nm to about 20 nm It should be particularly noted that thepressure at which the semiconductor device is fabricated issubstantially higher than the 10⁻⁸ torr associated with conventionaltechniques. Thus, the special metal seals and time consuming preparationsteps for the PVD tool are not required in the present invention.

In another embodiment, the metal protective layer 22 preferably has anaffinity for oxygen that is higher than that of the conductive layer 20and acts as a sacrificial target for the oxygen during the reflow of theconductive layer 20. In other words, it is believed that the metalprotective layer 22 readily combines with oxygen that is present in theconductive layer 20 and effectively pulls a substantial portion of theoxygen from the conductive layer 20, and thus, substantially preventsthe oxygen from oxidizing the conductive layer 20. As such it functionsas a "cap" to protect and substantially inhibit oxidation of theunderlying conductive layer 20. As previously discussed above, oxidationof the conductive layer 20 is undesirable because it substantiallyinhibits the conductive layer 20 from uniformly flowing into the opening14 during the reflow process and making proper contact with the interiorside walls of the opening 14, which can result in a defective integratedcircuit device. Furthermore, another possible advantage of the metalprotective layer 22 is that it may remove a substantial portion of anyoxygen from the conductive layer 20 that may have formed on theconductive layer 20 prior to the formation of the metal protective layer22. In a preferred embodiment, the metal protective layer 22 iscomprised of a metal selected from the group consisting of magnesium,yttrium, hafnium, cerium, scandium and zirconium.

In another embodiment, the metal protective layer 22 preferably has ahigh affinity for oxygen and acts as a sacrificial target for the oxygenduring the reflow of the conductive layer 20. It is believed that inthis embodiment the metal protective layer 22 readily combines withoxygen that is present in the environment surrounding the conductivelayer 20 and effectively pulls a substantial portion of the oxygen fromthe environment, and thus, substantially prevents the oxygen fromoxidizing the conductive layer 20. As such it functions as an oxygengetter to protect and substantially inhibit oxidation of the underlyingconductive layer 20. In a preferred embodiment, the metal protectivelayer 22 is comprised of a metal selected from the group consisting oftitanium and vanadium.

In yet another embodiment, the metal layer 22 may be capable of gettingthe oxygen from either the environment or for the conductive layer 20.In such embodiments, the metal protective layer 22 is comprised of ametal selected from the group consisting of a combination of metalspreviously discussed above and alloyed with aluminum alloys such asaluminum-copper, aluminum-silicon, or aluminum-copper-silicon. Forexample, the metal protective layer 22 may be comprised of eithertitanium or vanadium or magnesium, yttrium, hafnium, cerium, scandiumand zirconium, which may be alloyed with an aluminum alloy.

After deposition of the metal layer 22, the semiconductor device is thentransferred to either a reflow chamber 16d or a rapid thermal annealdevice 24 to be subjected to temperatures ranging between 350° C. to550° C., which are sufficient to reflow the conductive layer 20 suchthat it uniformly fills the opening 14. As previously stated, thedeposition tool may be of such a design that has only one chamber inwhich all phases of the deposition and annealing may be conducted. Afterdeposition and during the reflow process, it is believed that the metallayer 22 oxidizes and forms an oxidized metal that at least partiallydiffuses into the conductive layer 20 (FIG. 5). In such instances,research has shown that diffusion of titanium into aluminum-alloy actsto decrease the rate of electromigration damage accumulation in analuminum-alloy-copper conductive layer as discussed in the articleentitled "Roles of Ti-intermetallic compound layers on theelectromigration resistance of Al--Cu interconnecting stripes", J. Appl.Phys. 71, June 1992, pages 5877-5887, which is incorporated herein byreference. In some embodiments, the metal layer 22 may completelydiffuse into the conductive layer 20 or remain substantially on top ofthe conductive layer 20. In either embodiment, however, the metal layer22 serves as a target to which oxygen may bond, thereby preventingsubstantial oxidation of the conductive layer 20 such that it reflowsuniformly into the opening 14 and forms a reliable electrical contactpoint within the integrated circuit.

From the foregoing it is apparent that the present invention provides asemiconductor device that includes: (1) a substrate having a recesstherein, (2) a conductive layer located over at least a portion of thesubstrate and filling at least a portion of the recess and (3) a metalprotective layer at least partially diffused in the conductive layer.The metal has a higher affinity for oxygen than the conductive layer andthereby acts as a sacrificial target for oxygen during a reflow of theconductive layer to reduce oxidation in the conductive layer.

The present invention thereby introduces the broad concept of reducingthe oxidation that occurs in the conductive layer by providing a barrieror cap, in the form of the oxidized metal, that traps oxygen before itreaches the conductive layer or removes it from the conductive layer inthe event that the conductive layer partially oxidizes prior todeposition of the protective oxidizable metal layer. The presentinvention therefore allows a conductive plug to be formed reliablywithout requiring the exotic low pressure environment of the prior art.

The foregoing has outlined, rather broadly, preferred and alternativefeatures of the present invention. Additional features of the inventionwill be described hereinafter that form the subject of the claims of theinvention. Those skilled in the art should appreciate that they canreadily use the disclosed conception and specific embodiment as a basisfor designing or modifying other structures for carrying out the samepurposes of the present invention. Those skilled in the art should alsorealize that such equivalent constructions do not depart from the spiritand scope of the invention in its broadest form.

What is claimed is:
 1. A semiconductor device, comprising:a substratehaving a recess therein; a conductive layer located over at least aportion of said substrate and filling at least a portion of said recessto form a plug within said recess, said conductive layer susceptible tooxidation; and a metal protective layer at least partially oxidized anddiffused in said conductive layer, said metal protective layer having ahigh affinity for oxygen.
 2. The semiconductor device as recited inclaim 1 wherein said substrate comprises silicon.
 3. The semiconductordevice as recited in claim 1 wherein said metal protective layerdecreases the rate of electromigration damage accumulation in saidconductive layer.
 4. The semiconductor device as recited in claim 1wherein said meta, protective layer comprises a metal selected from thegroup consisting of:titanium, vanadium, magnesium, yttrium, hafnium,cerium, scandium, and zirconium, and said oxidized metal is alloyed withan aluminum alloy.
 5. The semiconductor device as recited in claim 4wherein said metal is selected from the group consisting of:titanium andvanadium.
 6. The semiconductor device as recited in claim 4 wherein saidmetal is selected from the group consisting of:magnesium, yttrium,hafnium, cerium, scandium, and zirconium.
 7. The semiconductor device asrecited in claim 1 wherein said metal protective layer is substantiallyoxidized by oxygen and diffused in said conductive layer.
 8. Thesemiconductor device as recited in claim 1 wherein said conductive layeris an aluminum-alloy layer.
 9. The semiconductor device as recited inclaim 1 wherein said conductive layer fills at least said portion ofsaid recess and forms a contact for said semiconductor device.
 10. Asemiconductor device, comprising:a dielectric substrate having a recesstherein; a conductive layer located over at least a portion of saiddielectric substrate and filling at least a portion of said recess toform a plug within said recess, said conductive layer susceptible tooxidation, and said plug in contact with either a gate, source or drainof said semiconductor device; and an oxygen-containing metal protectivelayer contacting and overlaying said conductive layer, saidoxygen-containing metal layer having a higher affinity for oxygen thansaid conductive layer.
 11. The semiconductor device as recited in claim10 wherein said dielectric substrate comprises silicon dioxide.
 12. Thesemiconductor device as recited in claim 10 wherein said metalprotective layer decreases the rate of electromigration damageaccumulation in said conductive layer.
 13. The semiconductor device asrecited in claim 10 wherein said oxygen-containing metal protectivelayer is comprised of a metal selected from the group consistingof:titanium, vanadium, magnesium, yttrium, hafnium, cerium, scandium,and zirconium,and is alloyed with an aluminum alloy.
 14. Thesemiconductor device as recited in claim 10 wherein said metal layer iscomprised of a metal selected from the group consisting of:titanium andvanadium.
 15. The semiconductor device as recited in claim 10 whereinsaid metal layer is comprised of a metal selected from the group aconsisting of:magnesium, yttrium, hafnium, cerium, scandium, andzirconium.
 16. The semiconductor device as recited in claim 10 whereinsaid oxygen-containing metal protective layer is substantially diffusedin said conductive layer.
 17. The semiconductor device as recited inclaim 10 wherein said conductive layer is an aluminum-alloy layer. 18.The semiconductor device as recited in claim 10 wherein said conductivelayer fills at least said portion of said recess and forms a contact forsaid semiconductor device.